Process control systems, like those used in chemical, petroleum or other processes, typically include one or more process controllers communicatively coupled to at least one host or operator workstation and to one or more field devices via analog, digital or combined analog/digital buses. The field devices, which may be, for example, device controllers, valves, valve positioners, switches and transmitters (e.g., temperature, pressure and flow rate sensors), perform functions within the process control system such as opening or closing valves and measuring process parameters. A central process controller receives signals indicative of process measurements made by the field devices and/or other information pertaining to the field devices, uses this information to implement a control routine and then generates control signals that are sent over the buses or other communication lines to the field devices to control the operation of the process control system. Field devices often initiate or generate process control alarms that signal when a parameter of the field device is outside an approved range. These alarms notify operators to help prevent accidents and/or are logged to help troubleshot the process control system.
Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts